Resonator element, resonator, and oscillator

ABSTRACT

A resonator element includes: at least one resonating arm extending, wherein the resonating arm has a mechanical resonance frequency which is higher than a thermal relaxation frequency thereof, the resonating arm has a groove portion, the groove portion includes a bottom portion, a first side surface that extends along the longitudinal direction of the resonating arm and comes into contact with the opened principal surface and the bottom portion, and a second side surface that faces the first side surface with the bottom portion disposed therebetween and comes into contact with the opened principal surface and the bottom portion, and the groove portion has a non-electrode region which extends from a part of the first side surface close to the bottom portion to a part of the second side surface close to the bottom portion and in which no electrode is provided.

REFERENCE TO CO-PENDING APPLICATIONS

This application is a Continuation of application Ser. No. 13/176,332filed Jul. 5, 2011. U.S. application Ser. No. 13/176,332 claims priorityto JP 2010-156577 filed Jul. 9, 2010. The disclosure of the priorapplications is hereby incorporated by reference herein in theirentirety.

BACKGROUND

1. Technical Field

The present invention relates to a resonator element, a resonator havingthe resonator element, and an oscillator having the resonator element.

2. Related Art

In the related art, a tuning-fork type piezoelectric resonator element(hereinafter referred to as a resonator element) in which a pair ofresonating arms alternately vibrates in the flexural vibration mode inthe direction towards or away from each other is widely used as aresonator element.

A loss of vibration energy when such a resonator element vibrates in theflexural vibration mode leads to an increase of the CI (CrystalImpedance) value or a decrease of the Q value and thus causesdeterioration of performances. Here, the CI value is a value whichserves as an indicator of the likelihood of oscillation, and the lowerit is, the more the resonator element is likely to oscillate. The Qvalue is a dimensionless number representing a vibration state, and thehigher it is, the more the resonator element vibrates stably.

Thermal conduction is considered as one of the causes of the loss ofvibration energy.

FIG. 4A is a diagram illustrating thermal conduction in a resonatorelement. As shown in FIG. 4A, a resonator element 151 includes twoparallel resonating arms 153 and 154 extending from a base portion 152.

When a predetermined voltage is applied to an electrode (not shown) insuch a state, the resonating arms 153 and 154 vibrate in the directiontowards or away from each other. When the resonating arms 153 and 154are moved away from each other, compressive stress acts on hatchedregions A (the outer root portions of the resonating arms 153 and 154),and tensile stress acts on hatched regions B (the inner root portions ofthe resonating arms 153 and 154).

When the resonating arms 153 and 154 are moved towards each other,tensile stress acts on the hatched regions A, and compressive stressacts on the hatched regions B.

At that time, temperature increases in the regions where compressivestress acts and decreases in the regions where tensile stress acts.

The resonator element 151 loses vibration energy due to heat transfer(thermal conduction) occurring due to equilibration of temperaturebetween a contracted portion of the resonating arms 153 and 154 wherecompressive stress acts and an expanded portion where tensile stressacts.

A decrease of the Q value caused by such thermal conduction is referredto as thermoelastic loss.

From the relationship between distortion and stress which is well-knownas a phenomenon of internal friction of a solid generally occurring dueto a temperature difference, the thermoelastic loss is described asfollows. In a flexural vibration-mode resonator element, when thevibration frequency changes, the Q value reaches the minimum at arelaxation vibration frequency fm (=½πτ; here, τ is a relaxation time).

The relationship between the Q value and the frequency is generallyexpressed as a curve F in FIG. 4B. In the drawing, the frequency atwhich the Q value reaches the minimum Q0 is a thermal relaxationfrequency f0 (=½πτ).

Moreover, a region (1<f/f0) on the high frequency side in relation to aboundary of f/f0=1 is an adiabatic region, and a region (f/f0<1) on thelow frequency side in relation to the boundary is an isothermal region.

FIGS. 5A and 5B are schematic diagrams showing a simplifiedconfiguration of a resonator element of the related art. FIG. 5A is aplanar diagram, and FIG. 5B is a cross-sectional diagram taken along theline C-C in FIG. 5A.

As shown in FIGS. 5A and 5B, a resonator element 100 includestuning-fork arms (hereinafter referred to as resonating arms) 102 and atuning-fork base portion (hereinafter referred to as a base portion)104. A groove 106 is formed on the upper and lower surfaces of each ofthe resonating arms 102, and electrodes 110 and 112 are disposed on theside surfaces of the groove 106.

The resonator element 100 also includes electrodes 114 and 116 whichhave different polarities and which are disposed on the side surfaces ofeach of the resonating arms 102 so as to face the electrodes 110 and 112(for example, see JP-A-2005-39767).

In the resonator element 100 disclosed in JP-A-2005-39767, as shown inFIG. 5B, a thermal conduction path between the contracted portion andthe expanded portion of the resonating arms 102 is narrowed in themidway by the grooves 106.

As a result, in the resonator element 100, a relaxation time τ up to theequilibration of the temperature of the contracted portion and theexpanded portion increases.

Therefore, in the resonator element 100, since the grooves 106 areformed, in the adiabatic region shown in FIG. 4B, the shape of the curveF itself does not change, but with a decrease of the thermal relaxationfrequency f0, the curve F shifts to the position of a curve F1 in thelower frequency direction. The curve F1 shows a state in which noelectrode is formed in the groove 106.

As a result, in the resonator element 100, the Q value increases asindicated by the arrow a.

However, in the resonator element 100, when the electrodes 110 and 112are formed in the grooves 106, the curve F shifts to the position of acurve F2, and the Q value decreases as indicated by the arrow b.

A thermal conduction path formed by the electrodes 110 and 112 can beconsidered as one of the reasons thereof.

That is, a conductive material such as an electrode material has higherthermal conductivity than a quartz crystal which is a piezoelectricmaterial used as a base material of the resonator element 100. In such aconductive material, electrons as well as phonons of metal carry thermalenergy.

Specifically, in the resonator element 100, as indicated by the arrowsin FIG. 5B, since thermal conduction is carried out by the electrodes110 and 112 as well as a quartz crystal, the relaxation time τdecreases, and with an increase of the thermal relaxation frequency f0,the curve F shifts to the position of the curve F2 in the higherfrequency direction.

In order to solve this problem, a configuration in which the electrodeson the bottom portion of the groove are removed to suppress thermalconduction by the electrodes on the bottom portion, thus increasing therelaxation time τ may be considered.

However, with progress in the miniaturization of the resonator element,it is difficult to sufficiently improve the relaxation time τ justthrough removal of the electrodes on the bottom portion of the groove.Thus, it is not possible to achieve a sufficient improvement of the Qvalue.

SUMMARY

An advantage of some aspects of the invention is to solve at least apart of the problems described above and the invention can beimplemented as the following forms or application examples.

Application Example 1

According to this application example of the invention, there isprovided a resonator element including: a base portion; and at least oneresonating arm extending from the base portion, wherein the resonatingarm has a mechanical resonance frequency which is higher than a thermalrelaxation frequency thereof, wherein the resonating arm has a grooveportion which is formed on at least one of the principal surfaces facingeach other and which extends in a longitudinal direction of theresonating arm, wherein the groove portion includes a bottom portion, afirst side surface that extends along the longitudinal direction of theresonating arm and comes into contact with the opened principal surfaceand the bottom portion, and a second side surface that faces the firstside surface with the bottom portion disposed therebetween and comesinto contact with the opened principal surface and the bottom portion,and wherein the groove portion has a non-electrode region which extendsfrom a part of the first side surface close to the bottom portion to apart of the second side surface close to the bottom portion and in whichno electrode is provided.

According to this configuration, in the resonator element, the grooveportion (synonymous with a groove) has a non-electrode region whichextends from a part of the first side surface close to the bottomportion to a part of the second side surface close to the bottom portionand in which no electrode is provided. Thus, it is possible to suppressthermal conduction by the electrodes in such portions.

As a result, in the resonator element, the transfer of heat from thecontracted portion to the expanded portion during flexural vibration isslowed down over a wider range of areas as compared to a configurationin which only the electrodes on the bottom portion of the groove portionare removed, for example. Thus, it is possible to further increase therelaxation time τ and to further decrease the thermal relaxationfrequency f0.

Through the decrease of the thermal relaxation frequency f0, in theresonator element, the curve F in FIG. 4B shifts to the vicinity of thecurve F1 in the lower frequency direction. Thus, it is possible toimprove the Q value in the adiabatic region.

Application Example 2

In the resonator element of the above aspect, it is preferable that theresonating arm includes an arm portion which is disposed close to thebase portion, and a weight portion which is disposed closer to a tip endof the resonating arm than the arm portion and which has a larger widththan the arm portion.

According to this configuration, in the resonator element, theresonating arm includes an arm portion which is disposed close to thebase portion, and a weight portion which is disposed closer to a tip endof the resonating arm than the arm portion and which has a larger widththan the arm portion. Through the effect of improving the Q value by theweight portion which increases the inertial mass, it is possible toshorten the resonating arm while maintaining the Q value, for example.

Therefore, in the resonator element, it is possible to achieve furtherminiaturization while maintaining the Q value.

On the other hand, when the weight portion is provided in the resonatorelement, for example, the amount of deformation during flexuralvibration increases as compared to a configuration in which no weightportion is provided. That is, the compressive and tensile stressoccurring therein increases.

However, in the resonator element, since thermal conduction by theelectrodes can be suppressed in the non-electrode region of the grooveportion, the transfer of heat from the contracted portion to theexpanded portion is slowed down. Thus, the thermoelastic loss can besuppressed more effectively when the weight portion is provided.

Application Example 3

In the resonator element of the above aspect, it is preferable that theresonator element includes a plurality of the resonating arms, and theplurality of resonating arms and the base portion form a tuning fork.

According to this configuration, the resonator element includes aplurality of the resonating arms and a base portion which form a tuningfork. Thus, it is possible to provide a tuning-fork resonator elementhaving an improved Q value.

Application Example 4

According to this application example of the invention, there isprovided a resonator including: the resonator element of the aboveaspect; and a package that accommodates the resonator element.

According to this configuration, since the resonator includes theresonator element of the above aspect, it is possible to provide aresonator having excellent vibration properties through the improvementin the Q value, for example.

Application Example 5

According to this application example of the invention, there isprovided an oscillator including: the resonator element of the aboveaspect; a circuit element that has an oscillation circuit oscillatingthe resonator element; and a package that accommodates the resonatorelement and the circuit element.

According to this configuration, since the oscillator includes theresonator element of the above aspect, it is possible to provide anoscillator having excellent vibration properties through the improvementin the Q value, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIGS. 1A and 1B are schematic diagrams showing a simplifiedconfiguration of a resonator element according to a first embodiment, inwhich FIG. 1A is a planar diagram, and FIG. 1B is a cross-sectionaldiagram of FIG. 1A.

FIGS. 2A and 2B are schematic diagrams showing a simplifiedconfiguration of a resonator according to a second embodiment, in whichFIG. 2A is a planar diagram, and FIG. 2B is a cross-sectional diagram ofFIG. 2A.

FIGS. 3A and 3B are schematic diagrams showing a simplifiedconfiguration of an oscillator according to a third embodiment, in whichFIG. 3A is a planar diagram, and FIG. 3B is a cross-sectional diagram ofFIG. 3A.

FIG. 4A is a diagram illustrating thermal conduction of a resonatorelement, and FIG. 4B is a diagram showing the relationship between arelaxation frequency of the resonator element and the minimum value ofthe Q value.

FIGS. 5A and 5B are schematic diagrams showing a simplifiedconfiguration of a resonator element of the related art, in which FIG.5A is a planar diagram, and FIG. 5B is a cross-sectional diagram of FIG.5A.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of the invention will be described withreference to the drawings.

First Embodiment

FIGS. 1A and 1B are schematic diagrams showing a simplifiedconfiguration of a resonator element according to a first embodiment, inwhich FIG. 1A is a planar diagram, and FIG. 1B is a cross-sectionaldiagram taken along the line D-D in FIG. 1A.

In FIG. 1A, hatching or shading is added to electrode parts for the sakeof convenience, and the electrode parts are simplified or partiallyomitted for better understanding of the drawing.

As shown in FIGS. 1A and 1B, a crystal resonator element 1 used as aresonator element is a resonator element of which the outer shape isformed by wet-etching, using a photolithography technique, awafer-shaped crystal substrate which is used as a base material andwhich is cut, for example, from crystal ore, at predetermined angles.

The crystal resonator element 1 includes a base portion 11, a pair ofresonating arms 12 and 13 extending approximately in parallel from thebase portion 11, a pair of notches 14 which is notched from both sidesof the base portion 11 in a direction (the left-right direction of thedrawing sheet) crossing the extension direction of the resonating arms12 and 13, and a pair of supporting portions 15 protruding from the baseportion 11 in the left-right direction of the drawing sheet, bentapproximately at a right angle towards the resonating arms 12 and 13,and extending along the resonating arms 12 and 13.

The pair of resonating arms 12 and 13 includes an arm portion 16positioned close to the base portion 11 and a weight portion 17positioned closer to the tip end of each of the resonating arms 12 and13 than the arm portion 16 and having a larger width than the armportion 16.

Moreover, the pair of resonating arms 12 and 13 includes a groove 18which is formed on principal surfaces 10 a and 10 b facing each other soas to extend along the longitudinal direction of the pair of resonatingarms 12 and 13 and which is cut along the arrangement direction (theleft-right direction of the drawing sheet) of the pair of resonatingarms 12 and 13 so that the resonating arms 12 and 13 have anapproximately H-shape in cross-sectional view.

The groove portion 18 includes a bottom portion 18 c including thedeepest portion, a first side surface 18 a that is formed along thelongitudinal direction of the resonating arms 12 and 13 and comes intocontact with the opened principal surfaces 10 a and 10 b and the bottomportion 18 c, and a second side surface 18 b that faces the first sidesurface 18 a with the bottom portion 18 c disposed therebetween andcomes into contact with the opened principal surfaces 10 a and 10 b andthe bottom portion 18 c.

The first and second side surfaces 18 a and 18 b are made up of aplurality of surfaces by etching anisotropy of a quartz crystal so thatan abrupt slope changes to a smooth slope as it approaches the bottomportion 18 c from the principal surfaces 10 a and 10 b.

The first and second side surfaces 18 a and 18 b may be made up of onesurface.

The bottom portion 18 c is illustrated to be inclined neither towardsthe first side surface 18 a nor the second side surface 18 b in FIG. 1B.However, the bottom portion 18 c is not limited to this, but may beinclined towards the first side surface 18 a or the second side surface18 b.

The crystal resonator element 1 includes excitation electrodes 20 and 21used as electrodes which are formed on the groove portion 18 of the pairof resonating arms 12 and 13, the principal surfaces 10 a and lob, andthe mutually facing side surfaces 12 a and 12 b, and 13 a and 13 b ofthe pair of resonating arms 12 and 13.

Next, the excitation electrodes 20 and 21 formed on the groove portion18 will be described.

As shown in FIG. 1B, the groove portion 18 has a non-electrode regionwhich extends from a part of the first side surface 18 a close to thebottom portion 18 c to a part of the second side surface 18 b close tothe bottom portion 18 c and in which the excitation electrodes 20 and 21are not provided.

In other words, the excitation electrodes 20 and 21 of the grooveportion 18 are formed in part of the first and second side surfaces 18 aand 18 b close to the principal surfaces 10 a and 10 b. That is, theexcitation electrodes 20 and 21 are formed in a range (L) of areas whichare in the midway of a portion extending from the principal surfaces 10a and 10 b towards the bottom portion 18 c.

The range L of areas in which the excitation electrodes 20 and 21 of thegroove portion 18 are formed is appropriately set, for example,considering a balance between the desired Q and CI values.

The range L of areas in which the excitation electrodes 20 and 21 areformed may be different in length between the first and second sidesurfaces 18 a and 18 b.

The range of formation areas of the excitation electrodes 20 and 21 inthe longitudinal direction of the groove portion 18 is appropriately setbased on requirements such as desired load capacitance sensitivity(frequency-load capacitance characteristics).

As shown in FIGS. 1A and 1B, the crystal resonator element 1 includesthe base portion 11 and the pair of resonating arms 12 and 13 which forma tuning fork, whereby a tuning fork-type crystal resonator element usedas a tuning fork-type resonator element is obtained. The crystalresonator element 1 is fixed to an external member such as a package ata predetermined position of each of the supporting portions 15.

In the crystal resonator element 1, when an external driving signal isapplied to the excitation electrodes 20 and 21 formed on the resonatingarms 12 and 13, the pair of resonating arms 12 and 13 alternatelyvibrate (resonate) in the flexural vibration mode at a predeterminedresonance frequency (for example, 32 kHz) in the directions indicated bythe arrows E and F.

The crystal resonator element 1 has a mechanical resonance frequency fwhich is set so as to be higher than a thermal relaxation frequency f0.In other words, in the crystal resonator element 1, a value obtained bydividing the mechanical resonance frequency f by the thermal relaxationfrequency f0 is set so as to exceed 1 (1<f/f0).

With this configuration, the crystal resonator element 1 vibrates in theflexural vibration mode in the adiabatic region (see FIG. 4B).

Next, the excitation electrodes 20 and 21 formed on the pair ofresonating arms 12 and 13 and the like will be described in detail.

On the pair of resonating arms 12 and 13 and the like, the excitationelectrodes 20 and 21 to which different-polarity external drivingsignals are applied are formed.

Therefore, the excitation electrodes 20 and 21 are formed to be spacedfrom each other so that they are not short-circuited.

As shown in FIG. 1E, the excitation electrode 20 is formed on the grooveportion 18 of the resonating arm 12, and the excitation electrode 21 isformed on both side surfaces 12 a and 12 b of the resonating arm 12.

The excitation electrodes 21 on both side surfaces 12 a and 12 b of theresonating arm 12 are connected to each other by a connection electrode22 (see FIG. 1A) formed on the weight portion 17.

On the other hand, the excitation electrode 21 is formed on the grooveportion 18 of the resonating arm 13, and the excitation electrode 20 isformed on both side surfaces 13 a and 13 b of the resonating arm 13.

The excitation electrodes 20 on both side surfaces 13 a and 13 b of theresonating arm 13 are connected to each other by a connection electrode23 (see FIG. 1A) formed on the weight portion 17.

The excitation electrode 20 on the principal surface 10 a side of thegroove portion 18 of the resonating arm 12 and the excitation electrode20 on the principal surface 10 b side are connected to each other by theexcitation electrodes 20 formed on both side surfaces 13 a and 13 b ofthe resonating arm 13.

On the other hand, the excitation electrode 21 on the principal surface10 a side of the groove portion 18 of the resonating arm 13 and theexcitation electrode 21 on the principal surface 10 b side are connectedto each other by the excitation electrodes 21 formed on both sidesurfaces 12 a and 12 b of the resonating arm 12.

As shown in FIG. 1A, the excitation electrodes 20 and 21 are led out upto the supporting portions 15 through the base portion 11, and thelead-out portions serve as mount electrodes 20 a and 21 a which are usedwhen the crystal resonator element 1 is fixed to the external membersuch as a package. The mount electrodes 20 a and 21 a are formed on bothprincipal surfaces 10 a and 10 b.

Next, an overview of a method of forming the excitation electrodes 20and 21 will be described.

The excitation electrodes 20 and 21 are formed in a desired electrodepattern shape by the following steps. First, an electrode material suchas Ni, Cr, Au, Ag, Al, or Cu is applied to approximately the entiresurface of the crystal resonator element 1 by a method such asdeposition or sputtering. Subsequently, a photosensitive resist isapplied so as to cover the applied electrode material and is subjectedto exposure and patterning in accordance with a desired electrodepattern shape using a photolithography technique. After that,unnecessary exposed portions of the electrode material are removed byetching (wet-etching), whereby the excitation electrodes 20 and 21having a desired electrode pattern shape are obtained.

Therefore, the non-electrode region of the groove portion 18 is formedwhen the unnecessary electrode material is removed by etching.

Moreover, thermal conductivity of a quartz crystal is about 6.2 to about10.4 W/(m·K), and thermal conductivity of Au, for example, used as theelectrode material of the excitation electrodes 20 and 21 is about 315W/(m·K) which is much larger than of a quartz crystal. The same can besaid for the other electrode materials (Ni, Cr, and the like).

As described above, in the crystal resonator element 1 of the firstembodiment, the groove portion 18 has the non-electrode region whichextends from a part of the first side surface 18 a close to the bottomportion 18 c to a part of the second side surface 18 b close to thebottom portion 18 c and in which the excitation electrodes 20 and 21 arenot provided.

Due to this configuration, in the crystal resonator element 1, it ispossible to suppress thermal conduction by the excitation electrodes 20and 21 in such portions (the non-electrode region).

As a result, in the crystal resonator element 1, the transfer of heatfrom the contracted portion to the expanded portion during flexuralvibration is slowed down over a wider range of areas as compared to aconfiguration in which only the excitation electrodes 20 and 21 on thebottom portion 18 c of the groove portion 18 are removed, for example.Thus, it is possible to further increase the relaxation time τ and tofurther decrease the thermal relaxation frequency f0.

Through the decrease of the thermal relaxation frequency f0, in thecrystal resonator element 1, the curve F in FIG. 4B shifts to thevicinity of the curve F1 in the lower frequency direction. Thus, it ispossible to improve the Q value in the adiabatic region.

Moreover, in the crystal resonator element 1, the resonating arms 12 and13 include the arm portion 16 which is disposed close to the baseportion 11, and the weight portion 17 which is disposed closer to thetip end of each of the resonating arms than the arm portion 16 and whichhas a larger width than the arm portion 16. Through the effect ofimproving the Q value by the weight portion 17 which increases theinertial mass, it is possible to shorten the resonating arms 12 and 13while maintaining the Q value, for example.

Therefore, in the crystal resonator element 1, it is possible to achievefurther miniaturization while maintaining the Q value.

On the other hand, when the weight portion 17 is provided in the crystalresonator element 1, for example, the amount of deformation duringflexural vibration increases as compared to a configuration in which noweight portion 17 is provided. That is, the compressive and tensilestress occurring therein increases.

However, in the crystal resonator element 1, since thermal conduction bythe excitation electrodes 20 and 21 can be suppressed in thenon-electrode region of the groove portion 18, the transfer of heat fromthe contracted portion to the expanded portion is slowed down. Thus, thethermoelastic loss can be suppressed more effectively when the weightportion 17 is provided.

Moreover, the crystal resonator element 1 includes a pair (two) ofresonating arms 12 and 13 and the base portion 11 which form a tuningfork. Thus, it is possible to provide a tuning fork-type resonatorelement having the above-described effects such as the improved Q value.

Second Embodiment

Next, a resonator having the crystal resonator element described abovewill be described as a second embodiment.

FIGS. 2A and 2B are schematic diagrams showing a simplifiedconfiguration of a resonator according to the second embodiment, inwhich FIG. 2A is a planar diagram, and FIG. 2B is a cross-sectionaldiagram taken along the line G-G in FIG. 2A. The electrodes of thecrystal resonator element are not illustrated for better understandingof the drawings.

As shown in FIGS. 2A and 2B, a crystal resonator 5 as a resonatorincludes the crystal resonator element 1 of the first embodiment and apackage 80 that accommodates the crystal resonator element 1.

The package 80 includes a package base 81, a shim ring 82, a cover 85,and the like.

The package base 81 has a recess so that the crystal resonator element 1can be accommodated therein, and connection pads 88 connected to themount electrodes 20 a and 21 a (not shown; see FIGS. 1A and 1B) of thecrystal resonator element 1 are provided in the recess.

The connection pads 88 are connected to wirings inside the package base81 so as to be electrically connected to an external connection terminal83 provided at the periphery of the package base 81.

The shim ring 82 is provided around the recess of the package base 81. Apenetration hole 86 is provided on the bottom of the package base 81.

The crystal resonator element 1 is attached to the connection pads 88 ofthe package base 81 by a conductive adhesive 84. In the package 80, thecover 85 covering the recess of the package base 81 is shim-welded tothe shim ring 82.

A sealing material 87 made from metal is filled in the penetration hole86 of the package base 81. The sealing material 87 is melted in adepressurized atmosphere and solidified to airtightly seal thepenetration hole 86 so that the inside of the package base 81 ismaintained in the depressurized state.

The crystal resonator 5 oscillates (resonates) at a predeterminedresonance frequency (for example, 32 kHz) when the crystal resonatorelement 1 is excited by an external driving signal supplied through theexternal connection terminal 83.

As described above, since the crystal resonator 5 includes the crystalresonator element 1, it is possible to provide a crystal resonatorhaving excellent vibration properties through the improvement in the Qvalue, for example.

Third Embodiment

Next, an oscillator having the crystal resonator element described abovewill be described as a third embodiment.

FIGS. 3A and 3B are schematic diagrams showing a simplifiedconfiguration of an oscillator according to the third embodiment, inwhich FIG. 3A is a planar diagram, and FIG. 3B is a cross-sectionaldiagram taken along the line H-H in FIG. 3A. The electrodes of thecrystal resonator element are not illustrated for better understandingof the drawings.

A crystal oscillator 6 as an oscillation has a configuration in whichthe crystal resonator 5 described above further includes a circuitelement. The same portions as those of the crystal resonator 5 will bedenoted by the same reference numerals, and description thereof isomitted.

As shown in FIGS. 3A and 3B, the crystal oscillator 6 includes thecrystal resonator element 1 of the first embodiment, an IC chip 91 as acircuit element having an oscillation circuit that oscillates thecrystal resonator element 1, and the package 80 that accommodates thecrystal resonator element 1 and the IC chip 91.

The IC chip 91 is attached to the bottom of the package base 81 and isconnected to other wirings by metal wires 92 such as Au or Al.

The crystal oscillator 6 oscillates (resonates) at a predeterminedresonance frequency (for example, 32 kHz) when the crystal resonatorelement 1 is excited by a driving signal supplied from the oscillationcircuit of the IC chip 91.

As described above, since the crystal oscillator 6 includes the crystalresonator element 1, it is possible to provide a crystal oscillatorhaving excellent vibration properties through the improvement in the Qvalue, for example.

In the respective embodiments described above, the supporting portion 15and the weight portion 17 of the crystal resonator element 1 may not beprovided.

The supporting portion 15 is not limited to a pair of supportingportions but may be provided in only one side.

In the respective embodiments described above, although the grooveportion 18 is provided on both principal surfaces 10 a and 10 b of theresonating arms 12 and 13, the invention is not limited to this, and thegroove portion 18 may be provided on only one of the principal surfaces(10 a or 10 b).

Moreover, in the respective embodiments described above, although thenumber of resonating arms 12 and 13 has been described to be one pair(two), the number of resonating arms is not limited to this but may beone or three or more.

Furthermore, in the respective embodiments described above, although theresonator element is formed of a quartz crystal, the invention is notlimited to this. For example, the resonator element may be formed of apiezoelectric material such as lithium tantalate (LiTaO₃), lithiumtetraborate (Li₂B₄O₇), lithiumniobate (LiNbO₃), lead zirconate titanate(PZT), zinc oxide (ZnO), or aluminum nitride (AlN); or a silicon havinga piezoelectric material such as zinc oxide (ZnO) or aluminum nitride(AlN) as a coating thereof.

The entire disclosure of Japanese Patent Application No. 2010-156577,filed Jul. 9, 2010 is expressly incorporated by reference herein.

What is claimed is:
 1. A resonator element comprising: a base portion; apair of resonating arms extending from the base portion along a firstdirection in plan view, a groove portion being arranged along the firstdirection on at least one of two principal surfaces, which have afront-and-rear relationship with respect to each other, wherein: theprincipal surface on which the groove portion is arranged includes oneprincipal surface portion and another principal surface portion whichsandwich an opening of the groove portion therebetween in plan view andare aligned along a second direction crossing the first direction, thegroove portion includes: a first side surface that is connected to theone principal surface portion and on which a first excitation electrodeportion is arranged at a side of the one principal surface portion, asecond side surface that is connected to the other principal surfaceportion and on which a second excitation electrode portion is arrangedat a side of the other principal surface portion, and an inner surfacethat is arranged between the first and second side surfaces; and thegroove portion has a non-electrode region in which no electrode isarranged, the non-electrode region including the inner surface andextending from an inner surface-side part of the first side surface toan inner surface-side part of the second side surface.
 2. The resonatorelement according to claim 1, wherein the resonating arm includes, inplan view, a weight portion and an arm portion which is disposed betweenthe weight portion and the base portion.
 3. The resonator elementaccording to claim 2, wherein a width of the weight portion is widerthan that of the arm portion along the second direction.
 4. Theresonator element according claim 1, further comprising: a supportportion that is connected to the base portion and is aligned with theresonating arm along the second direction.
 5. The resonator elementaccording claim 2, further comprising: a support portion that isconnected to the base portion and is aligned with the resonating armalong the second direction.
 6. The resonator element according claim 3,further comprising: a support portion that is connected to the baseportion and is aligned with the resonating arm along the seconddirection.
 7. The resonator element according to claim 1, wherein a pairof notch portions that are aligned along the second direction isarranged in the base portion.
 8. The resonator element according toclaim 2, wherein a pair of notch portions that are aligned along thesecond direction is arranged in the base portion.
 9. The resonatorelement according to claim 3, wherein a pair of notch portions that arealigned along the second direction is arranged in the base portion. 10.A resonator comprising: the resonator element according to claim 1, anda package that accommodates the resonator element.
 11. A resonatorcomprising: the resonator element according to claim 2, and a packagethat accommodates the resonator element.
 12. A resonator comprising: theresonator element according to claim 3, and a package that accommodatesthe resonator element.
 13. An oscillator, comprising: the resonatorelement according to claim 1; and a circuit.
 14. An oscillator,comprising: the resonator element according to claim 2; and a circuit.15. An oscillator, comprising: the resonator element according to claim3; and a circuit.
 16. An oscillator, comprising: the resonator elementaccording to claim 4; and a circuit.
 17. An oscillator, comprising: theresonator element according to claim 5; and a circuit.